This invention relates to an electronic musical instrument realizing a musical effect of gradually changing a pitch of a tone to be produced such as slur or portamento and, more particularly, to an electronic musical instrument in which a waveshape of an attack portion of a tone imparted with such pitch change is made different from a waveshape of an attack portion of that not imparted with such pitch change. Further, this invention relates to an electronic musical instrument in which control of an amplitude level is performed by taking into account an auditory tone level change in a case where the amplitude level of a tone is gradually changed with the pitch.
The effect according to which the pitch of a tone is changed smoothly from a tone pitch corresponding to a first key to a tone pitch corresponding to a second key is known as "slur" or "portamento" (hereinafter simply referred to as "slur"). Japanese Preliminary Patent Publication 139095/1984 discloses a system according to which a natural slur effect can be realized by smoothly changing not only the pitch but also the tone color of a tone. According to this publication, by adding and thereby combining tone signals of two channels with tone colors which are slightly different from each other at a level ratio which changes with time, a resulting timewise change in the tone color during imparting of slur is realized. More specifically, the tone color of one channel is a tone color which has been key-scaled in accordance with the tone pitch of a key which was being depressed until the present key has been depressed and the tone color of the other channel is a tone color which has been key-scaled in accordance with the tone pitch of the key which has been presently depressed. Accordingly, the tone color change during the slur period is not the tone color change proper to the slur but merely a smooth change in the tone color key-scaled by a precedingly depressed key to the tone color key-scaled by a presently depressed key.
In a natural musical instrument, there is a considerable difference in the tone color between an attack portion and a sustain portion of a tone and an attack portion of a new tone in the slur period also exhibits a unique tone color change. In the slur period, characteristics of the tone color of an attack portion of a new tone are closer to the tone color of a sustain portion than those of the tone color of a normal attack portion are. Such tone color change peculiar to the slur period was hard to realize by the prior art control technique which merely shifts the key-scaled tone color smoothly. Particularly, in an electronic musical instrument of a type which, for simulating the difference in the tone color in a tone between the attack portion and the sustain portion, employs a tone generation system which generates tone waveshapes of attack and sustain portions which have different tone color characteristics from each other, a tone waveshape having tone color characteristics of a normal attack portion is generated whether it is in the slur period or not and, accordingly, the imparting of smooth change in the key-scaled tone color as proposed in the prior art cannot restrain the tone color characteristics of the normal attack portion and therefore a tone color change proper to the slur period cannot be realized.
The above described publication discloses also a system according to which tone signals exhibiting the same slur pitch change are generated in two channels, the tone levels of the two tone signals are caused to change in such a manner that they have opposite characteristics and cross each other (crossfade). More specifically, as shown in FIG. 14a, the tone level of one channel is caused to fall relatively steeply at a predetermined decay rate from level L1 which was key-scaled in accordance with the tone pitch of a key which was being depressed until the present key has been depressed while the tone level of the other channel is caused to rise relatively gradually to level L2 which was key-scaled in accordance with the tone pitch of the present key.
In the tone level control as shown in FIG. 14a, however, the sum of the tone levels of the two systems falls as shown by the dotted line in the figure. This is because the decay rate is steeper than the attack rate. If the same rate is used for the decay rate and the attach rate as shown by FIG. 14b, the total tone level arithmetically becomes flat as shown by the dotted line but, in actual hearing, it gives the impression that the tone level somewhat drops in the portion in which the two levels cross.